1. Field of the Invention
The invention is in the field of laser systems and specifically in the field of short laser pulse generation.
2. Related Art
Optical isolators are used in laser systems to assure that light travels in one direction but not another. For example, in a ring laser system an optical isolator can be used to assure that light travels in one direction around the ring rather than in both directions. Optical isolators can also be used to prevent light from traveling back along a beam path from an amplifier to sensitive components of a laser system.
As illustrated in FIG. 1 an Optical Isolator 100 typically includes an Entrance Polarizer 110, a Faraday Rotator 120 and an Exit Polarizer 130. Light 140 can pass from Entrance Polarizer 110, through Faraday Rotator 120 and out through Exit Polarizer 130, but is prevented from passing in the reverse direction, e.g., through Exit Polarizer 130, Faraday Rotator 120 and then out through Entrance Polarizer 110. Optical polarizers of the type illustrated in FIG. 1 typically have transmission efficiencies in the range of 50 percent in the forward direction and 0.1 percent in the reverse direction. Further details of prior art optical isolators can be found in K Shiraishi, S Sugaya, & S Kawakami, “Fiber Faraday rotator”, Applied Optices 23 (7) [1 Apr. 1984] pp. 1103–1106.
One technique that makes use of optical isolators is chirped pulse amplification (CPA). As illustrated in FIG. 2, a CPA 200 includes a Pulse Source 210, a Pulse Expander 220, an Optical Isolator 100, a Pulse Amplifier 240 and a Pulse Compressor 250. Optical Isolator 100 is configured to prevent light, for example generated by spontaneous emission within Pulse Amplifier 240, from traveling back to Pulse Source 210. Light pulses generated using Pulse Amplifier 240 and Pulse Compressor 250 are optionally directed at a Target Material 260 for the purposes of material modification, ablation, or the like. Further information regarding CPA can be found in “Ultrafast lasers: Technology and Applications,” eds. M E Fermann, A Galvanauskas, G Sucha [Marcel Dekker, Inc., New York, 2003]; ISBN 0-8247-0841-5.
The systems of the prior art have a number of disadvantages including, for example, the inefficiency of Optical Isolator 100, the size of bulk optical components, and the sensitivity of Optical Isolator 100 to high peak power light and angular alignment. There is, therefore, a need for improved systems and methods in CPA systems.